Retrofocus-type lens system

ABSTRACT

A wide angle retrofocus lens system consists of seven lenses L1 through L7. Lens L1 is a positive meniscus with its convex surface directed to an object. Lens L2 is a first negative meniscus and lens L3 is a second negative meniscus, and both of the convex surfaces of these lenses L2 and L3 are directed to an object. Lens L4 is a positive and lens L5 is a negative lenses. Lens L6 is a positive meniscus having concave surface directed to an object. Lens L7 is a positive lens.

sou-bu SR Mori [54] RETROFOCUS-TYPE LENS SYSTEM [72] inventor: Ikuo Mori, Kawasaki-ski, Japan [73] Assignee: Nippon Kognki K.K., Tokyo, Japan [22] Filed: Jan. 20, 1970 [21] Appl. No.: 6,821

[30] Foreign Application Priority Date Feb. 8, 1969 Japan ..44/9( )06 52 0.5. CI. .350/214 511 Int. Cl .G02b 9/64,G02b13/04 5s FieldoiSearch ..3so/214,21s

[ 5 6] Reierences Cited UNITEDSTATESPATENTS 3,512,874 5/1970 Woltche .350/214 [451 Jan. 18, 1972 FOREIGN PATENTS OR APPLICATIONS 83,412 6/1964 France ..350/2l4 Primary Examiner.|ohn K. Corbin AnomeyHarry G. Shapiro [57] ABSTRACT A wide angle retrofocus lens system consists of seven lenses L, through L Lens L, is a positive meniscus with its convex surface directed to an object. Lens L, is a first negative meniscus and lens L, is a second negative meniscus, and both of the convex surfaces of these lenses L, and L, are directed to an object. Lens L is a positive and lens L is a negative lenses. Lens L. is a positive meniscus having concave surface directed to an object. Lens L, is a positive lens.

2 Claims, 11 Drawing Figures PATENTED JAN I 8 H72 SHEET 2 OF 3 COMA T LOWER PART OF STOP UPPER PART OF STOP illtjj v l T LATERAL SPHERICAL ABERRATION COMA OF -30 COMA OF -40 FIG.2(B) FIG.2(C) F|G.2(D) F|G.2(E)

sPHERmL ASTIGMATISM AT ASTIGMATISM DISTORTION MAGNIFICATION ABIERRATION RATIO O V30 T- A5 A. I

"| O I 3 -2 O INVENTOR. IKUO NOR! ATTORNEY PAIEmEnJmemz 3.635546 SHEET 3 BF 3 FIG. 4(A) LATERAL SPHERICAL ABERRATION COMA OF -3o COMA OF 38 FIG.4(B) F|G.4(C) FIG.4(D)

ggigf- ASTIGMATISM DISTORTION INVENTOR. IKUO MOB! BY M ATTOR- EY RETROFOCUS-TYPE LENS SYSTEM The present invention relates to a lens system and more particularly a wide-angle retrofocus-type lens system.

In the wide-angle retrofocus-type lens, the larger the distance from the first lens to the stop position becomes, the better the aberrations may be corrected. Especially the two aberrations of the astigmatism and the curvature of the field present this tendency strongly.

However, when the distance is increased, the diameter of the first lens must be increased so that the diameter of a filter attached to the lens system must be inevitably increased.

There may be no problem when the lens system is mounted to a small-sized camera such as 35-mm. cameras, but when the lens system is mounted to a large-sized single-lens reflex camera such as 6X6 or 6X7 cm., the operation will become very difficult because the diameters of the lens system and a filter attached thereto are exceedingly large.

Accordingly, the primary object of the present invention is to provide an improved wide-angle retrofocus-type lens system which can eliminate the above described defects.

Another object of the present invention is to provide a wideangle retrofocus-type lens system compact in size having its aberrations reduced to the minimum.

In brief, the wide-angle retrofocus lens system in accordance with the present invention comprises a positive meniscus lens having its convex surface directed toward an object, two negative meniscus lenses each having its convex surface directed toward the object, a positive lens, a negative lens, a positive meniscus lens having it concave surface directed toward the object and a positive lens. In the lens system, the following conditions must be fulfilled:

where f the compound focal length of the lens system;

f the compound focal length of the diverging system (the first three lenses);

d thickness of lens and air space;

R radius of curvature; and

1 the optical separation of the surfaces 1 and 7 (d,-t-d,-l-d;,+d,-t-d +11 The two most remarkable advantages of the present invention are as follows: I. The diameters of the lens system as well as the filters thereof may be remarkably reduced. For example, the diameter of the filter is reduced only to approximately 0.6 of that of the conventional lens system having the same field angle with that of the lens system of the present invention. 2. The aberration of the curvature of the field, astigmatism and comma are corrected in a satisfactory manner even when the field angle is 80, and the lens system which will be used suitably and advantageously for the large-sized single-lens I FIGS. 2(A)-2(C) show the aberration curves thereof;

FIG. 3 is a sectional view of a second embodiment of the present invention in which the lens (L, in FIG. I) is replaced with a single lens; and

FIGS. 4(A)-4(D) show the aberration curves thereof.

Referring to FIG. I, a retrofocus-type lens in accordance with the present invention comprises a positive meniscus lens L, with its convex surface being directed toward an object, a first negative meniscus lens L, and a second negative meniscus lens L, both of the convex surfaces of the negative meniscus lenses being directed toward the object, a positive lens L a negative lens L a positive meniscus lens L. with its concave surface being directed toward an object and a positive lens L And the following conditions are satisfied:

f the compound focal length; f the compound focal length of the diverging lens system 1, L2, and a;

d thickness of the lens and the air space between the lenses;

R radius of curvature of the lens; and

l the optical separation of the surfaces 1 and 7 (d ,+d,+d;-l-d.-l-d +11).

In order to provide a retrofocus-type lens system compact in size, the distance between the first or outennost lens to the stop position must be reduced. For this purpose, it is the best method to reduce the airspace, but a desired back focal length is not obtained only when the air space is reduced.

Therefore, according to the present invention, the diverging system has a very strong refracting force (Condition I), thereby ensuring the miniaturization and the long back focal length of the lens system. However, the problem is the increase of the negative distortion. In order to correct it, the positive meniscus lens is arranged at the outermost or first position of the lens system according to the present invention. In such a usage, the positive meniscus lens has a tendency of increasing its diameter so that in order to prevent it, it is preferable that the opposing surfaces between the positive meniscus lens L, and the negative meniscus lens L, have the following relation l.8 R,jR 2.8 so that the air space therebetween may be not increased too much around the peripheries of the lenses. When the conditions I is not satisfied, that is when fA is less than the lower limit 0.6f, the negative distortion will be increased. On the other hand when fA is in excess of the upper limit 0.9f, the back focal length will be reduced. When the optical separation of the surfaces 1 and 7 is lower than the lower limit of the condition II, the back focal length will be reduced. On the other hand, when the sum is in excess of the upper limit 0.651, the object of the present invention for miniaturizing the lens system cannot be achieved. The diverging system consisting of a positive and negative meniscus lenses is known in the art, but when the conditions of the present invention must be satisfied in this diverging system, the radius of curvature of the concave surface of the negative meniscus lens must be made exceedingly small, thereby remarkably increasing the spherical aberration and coma. Therefore, the diverging system must be comprised of at least two negative meniscus lenses. The condition 111 is for eliminating the residual astigmatism which tends to occur at the center portion of the film plane when the lens system is miniaturized. The condition IV is necessary for correcting the sine condition which tends to be deteriorated in the positive direction due to the strong refracting force of the diverging system. Otherwise, the comma aberration is remarkably increased in the positive direction by the slanting light ray passing above the stop position related to the deterioration of the sine condition in the positive direction. Then correcting the errors by other surfaces becomes too difficult to carry out so that the condition lV must be satisfied.

When the f-number is 4, the angle of view 80 and the focal length FIDO in the lens system shown in FIG. I, the design data are as follows:

Back focal length l36.96 fA=-69.9

TABLE I Curvature Curvature oi oi Spherical Meridional Sagittal Distoraberration Coma Image Image tion 1 0.041 0. 052 0.416 0. 285 0. 360 2 0.001 0. 006 0. 002 0. 078 0. 663 3 0. 013 0.021 0. 372 0. 308 0.470 4 6. 484 0. 410 0. 906 0. 852 0. 065 5 3. J72 0. 479 0. 726 0. 611 0.074 6 26. 414 1.677 1.300 1.087 0. 069 7 18. 065 1. 549 0. 903 0. 660 0. 053 8 0.000 0.000 0.000 0.000 0.000 It 6. 835 2. 166 l. 491 1.110 0. 36b 10 7.330 1.635 L666 -0. 1130 0200 ll 3.l60 2. 101 3.603 1.370 0. 730 2 0. 001 0.006 0. 636 0. 000 (I. 430 I3 4. 334 0. 673 1.031 0. 821 0. 128 0. 001 0. 000 0. 173 0. 054 0. 363 11.187 -1.082 0.824 0.614 0.060

Back focal length 138.82 fA='--80.S6

R, d, n, vd, B.f and fA are same to those described hereinabove.

FIG. 4(A) shows the coma, FIG. 4(B), the spherical aberration; FIG. 4(C), the astigmatism; and FIG. 4(D), the distortion of the lens system above in FIG. 3.

What is claimed is:

I. A retrofocus-type lens system comprising a positive meniscus lens (L the convex surface of which is for direction toward an object to be photographed, negative meniscus lenses (L L the convex surfaces of which are for direction toward the object, a positive lens (L,), a negative lens (L a positive meniscus lens (L the concave surface of which is for direction toward the object, and a positive lens (L of which the detailed data is as follows:

where R radius of curvature;

d thickness of lens and air gap;

n index of refraction of glass used;

vd= Abbe number of glass used;

Bf= Back focal length; and

f/A compound focal length of the diverging system consisting of L and L Ii 2 d the optical separation of the surfaces 1 and 7 (d,-l-d,+d;,-l-d.+d +d 2. A retrofocus-type lens system comprising a positive meniscus lens (L the convex surface of which is for direction toward an object to be photographed, negative meniscus lenses (L L the convex surfaces of which are for direction toward the object, a positive lens (L), a negative lens (L a positive meniscus lens (L the concave surface of which is for direction toward the object, and a positive lens (L of which the detailed data is as follows:

the optical separation of the surfaces 1 and 7 (d +d,+d,-+-d l-d +d UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECMQN Patent No- 5, 546 Dated January 18, 1972 Inventor(s) IkuO MOI'i It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, beginning line 75 insert Back focal length 136. 96

Column 6, line 2 change "01 to d +8 line 10 change '1. 6988" to 1. 6968 Signed and sealed this 13th day of March 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 5 FORM PO-105O (10-69) USCOMM-DC 6O376-F'69 UYS GOVERNMENT PRINTING OFFICE: 1969 0-366-33A 

1. A retrofocus-type lens system comprising a positive meniscus lens (L1) the convex surface of which is for direction toward an object to be photographed, negative meniscus lenses (L2, L3) the convex surfaces of which are for direction toward the object, a positive lens (L4), a negative lens (L5), a positive meniscus lens (L6) the concave surface of which is for direction toward the object, and a positive lens (L7) of which the detailed data is as follows:
 2. A retrofocus-type lens system comprising a positive meniscus lens (L1) the convex surface of which is for direction toward an object to be photographed, negative meniscus lenses (L2, L3) the convex surfaces of which are for direction toward the object, a positive lens (L4), a negative lens (L5), a positive meniscus lens (L6) the concave surface of which is for direction toward the object, and a positive lens (L7) of which the detailed data is as follows: 